1. Field of the Invention
The present invention is in the field of electronics and pertains particularly to methods and apparatus for integrating multiple batteries to form a battery pack.
2. Discussion of the State of the Art
In the field of electronics, newer lithium-based batteries, both primary (non-rechargeable) and secondary (rechargeable) have been developed that have much higher energy density ratings than the standard Nickel Cadmium (NiCd) or Nickel Metal Hydride (NiMH). At the time of this writing, there are a few varieties of Lithium-based batteries. These are Lithium Ion (Li-Ion) batteries and Lithium Ion Polymer (LiPo) batteries. Li-Ion batteries are typically provided in the form of a cylindrical cell. LiPo batteries are typically provided in the form of a prismatic or rectangular cell. Both Li-Ion and LiPo have similar battery chemistry with 3.7V/cell being the nominal voltage. These batteries require certain handling criteria to help avoid safety concerns such as over current, over voltage, and under voltage conditions. Failure to heed handling and charging instructions may result in a fire.
A battery may comprise of one or more cells of a given battery chemistry. For example, a 3.7V Li-Ion battery consists of a single Li-Ion cell. A 7.4V Li-Ion battery consists of two Li-Ion cells, and so on. Li-Ion cells are usually fabricated within a cylindrical metal component. Standard sizes may vary but include the 18650 model size of 18 mm diameter×65 mm in length. These batteries include an integral blow-off valve to handle over pressure due to overcharging.
Cylindrical Li-Ion cells may be provided with or without connection tabs. Connection tabs are generally soldered or spot-laser-welded to each end of the battery. LiPo battery cells are fabricated in a variety of shapes and sizes. These batteries are often used in portable power applications where a custom battery shape is beneficial or necessary, such as with a smart phone, an iPad, an iPod, or the like. Prismatic cells are packaged in a sealed plastic-type ‘bag’ enclosure. Prismatic cells are always supplied with two connection tab terminals, a positive terminal and a negative terminal.
Lithium batteries must be handled with care at all times as described further above. The basic critical limits per battery cell are battery over-voltage and battery charge and discharge currents. Lithium-based battery cells lack any protection circuits. One terminal, typically the positive terminal, is taped over or otherwise insulated at the point of sale to prevent any sort of electrical contact with anything that might conduct a current. A short between the positive and negative terminals of a Li-Ion or LiPo cell may immediately result in a short circuit, large currents, and possibly fire.
Therefore, what is clearly needed is a battery integration module or pack that solves the above limitations while providing safe access to electrical power.